This invention relates to the field of non-disconnectable junction devices intended to join together the ends of conveyor belts. For simplification purposes, the term xe2x80x9cconveyor beltxe2x80x9d in this description will be used to refer to conveyor belts and power transmission belts.
In the past, junction devices have been used with a general H-shaped section that can be fixed on the ends of a conveyor belt. These junction devices comprise two pairs of attachment flanges corresponding to the flanges of the H-shaped section and an intermediate central part that corresponds to the web of the H-section. One of the ends of the conveyor belt is inserted between one of the pairs of flanges, and the other end is inserted between the other pair. The flanges are attached to the ends of the conveyor belt by means of rivets, nails, crampons, screw-nut systems or by cold gluing or flat vulcanisation of the flanges in contact with the flat outside surfaces of the conveyor belt engaged between the flanges. These junction devices are made of a flat elastic flexible material such as vulcanised rubber, or a synthetic material such as polyurethane, and they contain a built-in reinforcement. However, the proposed reinforcements were made of an ordinary fabric, and were not capable of sufficient elongation to pass over the conveyor belt drive or return rollers without causing damage to the junction device installed at the ends of the conveyor belt.
The applicant for this patent has deposited a previous patent divulging the use of fabrics or knits. For fabrics, he described the use of fabrics comprising a deliberately loosely woven weft so that this weft in the longitudinal direction would deform until the weft threads become tightened and transmit tension, in order to absorb the different path distances that occur in the junction device when passing over the drive or return rollers around which the conveyor belt on which the junction device is installed passes without any damage being caused, the loose threads thus tightened would be capable of transmitting a tension force for which they are designed, then being brought back together by the constituent material. The applicant for this patent had also described the use of platelets or washers in the flanges of the junction devices designed to fix these devices to the ends of the conveyor belt, these platelets or washers comprising a hole through which nails, rivets, crampons, screws or any other devices with a rod designed to pass through a flange, the conveyor belt and then the other flange could be inserted, and being fixed on the other side of the other flange. In a version comprising cables, the washers were anchored to the reinforcement composed of cables, through loops formed by these cables and surrounding the perforated washers. In the case of a fabric or knitted reinforcement, holes were formed in the flanges and consequently in the reinforcement.
Despite the essential improvements included in the solutions proposed in the past by the applicant for this patent application, it was found in practice that there were still limitations on the use of the resulting junction devices, namely:
fabrics with weft butt joints were not sufficiently flexible in the direction of motion of the conveyor belt when passing over some drive or return rollers encountered in practice,
the construction of a channel-shaped conveyor belt was too difficult due to the excessive stiffness of the junction device preventing it from satisfactorily following the conveyor belt when the edges of the belt were lifted up for bulk transport purposes,
in some cases, attachment of the flanges using single perforated reinforcing washers with conventional attachment means caused tearing of the reinforcements at the location of the holes formed in the reinforcements, and the resistance of the reinforcements was reduced due to the large number of small lesions caused by these holes,
junction devices made by moulding or by injection required a different mould for each thickness of conveyor belt used in practice, for their production, and consequently they had to be manufactured in very small series which increased the cost price, and the manufacturing, storage and distribution price.
The purpose of this invention is to propose solutions to the problems described above.
The applicant discovered that to solve the problem of the necessary extendibility of the flanges of junction devices provided with fabric reinforcements it was useful if the texture of the fabrics was loose or if it was strongly curved in weft and in warp. The applicant also discovered that with these fabrics with a loose warp and weft, it was possible to use fabrics in one or several layers in two different arrangements.
According to a first arrangement, the reinforcing fabrics are arranged so that the direction of the warp or the weft is parallel to the longitudinal direction of the junction devices, in other words by convention along the direction of motion of the conveyor belt that must be fixed to it, independently of the effective dimensions of the junction devices. Similarly in this description, by convention, the transverse direction of the junction device will be the direction perpendicular to the longitudinal direction defined above.
According to a second arrangement, the reinforcing fabrics in which the warp and the weft are loosely woven, are arranged such that the warp or the weft are equally loose and form an angle from the longitudinal direction of the junction device, regardless of whether the fabric is arranged in a single layer or in several layers. The optimum angle is found to be approximately 45xc2x0.
All that has been said above about loosely woven fabrics that are loose in warp and in weft, is also applicable for knits, that can be knitted loosely in warp, while adding a weft that can be inserted loosely.
Using the solutions mentioned above, the applicant obtained reinforcements sufficiently flexible to accommodate all elongation necessary for the conveyor belts to pass over all rollers that have been encountered in practice.
However, the problems caused by attachment of the flanges onto the ends of conveyor belts, and particularly the problem caused by lesions in the reinforcements, have not been solved despite the improvements to the structure of the reinforcement described above.
Therefore, the applicant has designed and developed improved washers that are put into place so as not to cause any damage (or in any case only slight damage) to the woven or knitted reinforcement. These washers comprise a recess that will contain the head of the attachment means with a stem, this recess being extended as a tubular part, at least in some of the washers. The washers also comprise at least one pin oriented in the same direction as the recess, in other words towards the reinforcement, this pin being located at the periphery of the washer and preventing rotation of the washer. The reinforcement, composed of one or several layers of fabric or knit as described above, is arranged around the tubular part extending the recess perpendicular to the general plane of the washer such that the edges of the reinforcement surrounding the tubular part are raised along the tubular part also forming a right angle, or approximately a right angle, with the plane of the reinforcement. These raised edges of the reinforcement bond to the tubular part. With this conformation of the washer and its arrangement in the reinforcement, the reinforcement is not perforated consequently causing wires to be cut in the fabric or the knit, and instead the threads are simply separated. Obviously, it is possible that a thread can break but the lesion thus caused is much less serious than the lesion created by conventional holes cut in flanges by drilling or by punching. Furthermore, the diameter of the washer can be reduced due to the fact that the washer not only bonds flat to the reinforcement through its head, but it also bonds in the perpendicular direction through the outside surfaces of the tubular part to the raised edges of the reinforcement. Thus, the anchorage of the recess in the flange of the junction device is particularly good.
Furthermore, due to the fact that the head of the washer head is small, if necessary it may pivot by a few degrees from the perpendicular to the general plane of the flange considered due to the articulation caused by the fact that the angle formed between the plane of the majority of the reinforcement and its raised edges bonding to the tubular part of the washer, this capability being useful in combination with the attachment means described below. These washers thus shaped and placed are arranged in the flanges of the lower part.
In the upper part, the washers consist only of a perforated recess without a tubular part, and in the lower part the washers consist of a recess extended by a tubular part as described above. The tubular part of these washers is threaded on the inside. This arrangement enables the use of screws as an attachment means. A screw, preferably a self-tapping screw, inserted into the washers without a tubular part is screwed into the end of the conveyor belt after being inserted into the space between the two flanges of the same pair, until it stops in contact with the intermediate part of the junction device; the screw then enters the threaded hole in the tubular part of the washer in the other flange, the relative mobility of the tubular part with respect to the perpendicular to the general plane of the washer enabling mutual self-centering of the screw in the tubular part. By screwing into the tapped thread, the screw exerts a high tension on the washer through the tubular part of the washer, this tension causing efficient clamping of the two flanges in contact with the plane outside surfaces of the end of the conveyor belt. This tension is transmitted to the lower flange, both through the head of the washer and the outside surface of the tubular part to which the reinforcement is bonded, the surfaces of the reinforcement and the tubular part working in shear.
In practice, the washers and consequently the screws, are arranged to be staggered on the surface of the flanges to optimise distribution of the tightening points.
Additional improvements are explained later as part of the description of a preferred embodiment with reference to the figures in the drawing illustrating this description.
However, due to the excellence of these flange attachment means to the ends of the conveyor belt, the applicant has been able to solve the other problem that occurred initially, namely the problem of the large number of moulds and moulded products necessary for the various thicknesses of conveyor belts. The solution found consists of making junction devices in three separate parts; one part forming the left and right top flanges in a single piece, apart forming the left and right bottom flanges in a single piece, and an intermediate part corresponding to the central web of the H-section.
The top part comprises two or several washers of the type provided with a tubular part, smooth on the inside, built into the top part on a median line forming an imaginary separation between the left flange and the right flange, the tubular parts of the washers facing downwards.
The bottom part is provided with two or several washers of the type comprising a threaded tubular part built into the bottom part on a median line forming an imaginary line separating the left flange from the right flange, the tubular threaded parts facing upwards.
It should be clear that the concepts of top and bottom are only useful for the purposes of the description and that in practice they can be inverted.
The intermediate part is parallelepiped shaped, and it can be produced, stored and distributed in several different heights comprising built in bushings that pass through them in the direction of the height, and that have the same spacing as the built-in washers in the middle of the top and bottom parts, so that the built-in washers can be aligned with the top and bottom parts when the top and bottom parts are arranged on each side of the intermediate part. The diameters of the cylindrical assemblies composed of the tubular parts of the washers comprising raised parts of the reinforcement bonding to their outside surface and layers of rubber or synthetic material between which the reinforcement layers are sandwiched, are such that these cylindrical assemblies can be inserted in the corresponding bushings in the intermediate part. Thus, it is possible to screw in screws with a head that fits in the recesses of the inserts with a smoothed tubular part, the threaded stems of the screws passing through the bushings without screwing into them since the inside diameter of the bushing is greater than the outside diameter of the screw by at least twice the thickness of the reinforcement surrounding the tubular part of the washer. The screws are then screwed into the tapped thread of the threaded tubular parts of the built-in washers as described above, in the middle area of the lower parts.
Additional improvements will be described later in relation to a preferred embodiment illustrated by the figures.
Tests carried out showed not only the excellent quality of this assembly according to the invention, but manufacturing is also very much simplified compared with a junction device made from a single piece by moulding or by injection. The manufacture of the reinforcements and their arrangement in the moulds is very much simplified by making an upper part with a left upper flange and a right upper flange separately and connected by a median part, a lower part comprising a lift lower flange and a right lower flange connected by a median part, and an intermediate part provided by bushings that can be made in several different lengths.